1. Field of the Invention
The present invention relates to a disc type cylinder lock which is capable of effecting locking and unlocking operations of an equipment such as a door and the like without any anxiety, in which a key is pulled out by reversing locking tumbler discs that are at an incompletely unlocked position.
2. Description of the Prior Art
In a disc type cylinder lock of the prior art, as disclosed in U.S. Pat. No. 2,217,047 and U.S. Pat. No. 2,862,380, discs inserted into an inner cylinder are only locking tumbler discs which only perform locking and unlocking operations relative to inner and outer cylinders.
However, such a disc arrangement cannot prevent the key from rotating in a state where insertion of the key is not yet accomplished, and consequently the innermost locking tumbler disc may be left in a non-rotated position. For this reason, a through-groove is never formed at peripheries of all of the locking tumbler discs, so that a side bar cannot move toward the inner cylinder, whereby the inner cylinder cannot be unlocked with respect to the outer cylinder. In such a situation of incomplete unlocking, as the key is unable to further rotate, an operator is liable to make a misunderstanding that the unlocking operation is finished, and then the operator may undesirably pull out the key by reversely rotating the locking tumbler discs.
If the key is pulled out in a state where key-holes of the locking tumbler discs are never aligned with each other, at the next time of key insertion, the tip of the key is likely to impinge upon one or more locking tumbler discs not rotated at the first operation. In this instance, in order to completely insert the key up to the innermost locking tumbler disc, the operator must shake the key at anytime when encountering such an impingement condition, so that it is impossible to get a smooth locking operation.
On the other hand, in a detent mechanism of the prior art, an inner cylinder provided with a radial hole in its rear end portion. A small detent ball and a compression coil spring are inserted into said radial hole. The detent ball engages with one of two recessions formed in the peripheral surface of an outer cylinder, when the inner cylinder is rotated to the unlocking position or the locking position. It is necessary to provide a surplus space for an exclusive use of the detent mechanism.